The present invention relates to a method of recording information on an optical disk by forming recording marks that are different in physical property from other portions on a recording medium. The invention also relates to laser driving apparatus and optical disk apparatus (hereinafter referred as an optical disk drive).
There are many recordable optical disk media such as CR-R/RW, DVD-RAM, DVD±R/RW, Blu-ray Disk, and HD-DVD. These media including dual-layer media having two recordable layers have enjoyed wide acceptance. Corresponding optical disk drive that are widespread are so-called DVD Super Multi drives corresponding to reading and writing to and from CD-R/RW, DVD-RAM, and DVD±R/RW. It is contemplated that the ultimate Super Multi drive to which functions of coping with Blu-ray Disk and HD-DVD are added will be developed in the future. At the same time, optical disk drive are required to have reduced sizes, lower costs, and reduced power consumption.
In this way, to cope with plural media conforming to different standards, complicated Write Strategies are necessary. One of the write strategies which are most complex today (pulse trains consisting of many power levels) is a write strategy for 4.7 GB DVD-RAM. This is internationally standardized by ISO/IEC DIS 17892:2003. A technique for improving the compatibility of 4.7 GB DVD-RAM write strategies is described in JP-A-2003-187443.
FIG. 2 illustrates a write strategy that is adapted for 4.7 GB DVD-RAM and described in FIG. 1 of the above-cited JP-A-2003-187443. As can be seen from the figure, a pulse train consisting of a first pulse, multiple intermediate pulses, a last pulse, and cooling pulses is used to form one recording mark. With respect to power levels, there are 4 values of power in total. That is, a power level (peak power) for writing is used. A power level (bias power 1) for erasure is used. A power level for the cooling pulses (bias power 2) is used. A power level for the bottom of the intermediate pulses (bias power 3) is used.
There are two major systems which correspond to such write strategies and are adapted for laser driver ICs capable of multi-X speed writing.
The first system is described in JP-A-2005-339790. This uses a laser driver installed on a head. The laser driver incorporates a register for setting of power and a logic circuit for creating pulses. Therefore, fundamentally, control signals are only a clock signal, write data signal (NRZI), and a serial data signal for register I/O. There are the advantages that the number of control signal lines is few and that skew adjustment of pulses is not necessary. However, the circuit configuration is complicated and the power consumption tends to be large.
The second system is described in JP-A-11-354893 and uses a laser driver mounted on a head but the laser driver does not have any large-scale logic circuit. An example of the configuration is shown in FIG. 3. Required control signals include voltage level (which can be current levels) lines for setting laser powers and switching instruction lines for selectively turning on and off current switches corresponding to the power levels to control the pulse widths and the timings. To cope with multi-X speed writing, the switching instruction lines for controlling one current switch consist of one pair of differential signals. As a differential signal system, a well-known LVDS system is used. This system has the disadvantages that there are many control signal lines and that adjustment of skew between the switching instruction lines is required. However, the circuit configuration is simplified. Reduced costs and power consumption can be easily achieved.